The authority's deputy chief executive quality assurance, Grant Klinkum, said NZQA assessors disagreed with 80 percent of the grades they double-checked in two courses at the college in September last year.

He said NZQA found further problems in two other business programmes this month and as a result the college had agreed to stop teaching the Level 5 and Level 6 courses.

"The first action was to stop any new students being enrolled into the first two business programmes where we found problems, and then when we found problems with two further programmes they agreed at that point to stop teaching those," Dr Klinkum said.

Dr Klinkum said NZQA would have taken "appropriate action" to protect students if the college had not agreed to stop teaching the courses.

"We have found poor quality assessment, examples of plagiarism and spin-botting," he said, the latter referring to the use of computer programs that hide plagiarism.

He said the college also had poor record-keeping and was not keeping to its schedule for assessment and moderation.

Dr Klinkum said the college had 1000 students in total, and its other courses included preparation for university study, English language and a Level 7 business diploma.

"We are looking at other programmes they offer as well, but at this stage we only have evidence about the four business programmes that we've already taken action over.

"We will look more widely and if we do find further problems then we will take appropriate action."

Dr Klinkum said the 300 students affected by the course closures would be re-tested before they started at their new education provider, New Zealand Management Academies.

"What we're trying to do is establish whether students need to re-sit any credits that they've previously been awarded or whether they need to be re-taught an entire course or an entire programme," he said.

"It will be the responsibility of the New Zealand National College to pay for the cost of any re-testing, English language testing or re-teaching that is required as a consequence of the poor quality."

A private tertiary institution group says there were lots of red flags the Qualifications Authority missed in letting disgraced Linguis International Institute operate as long as it did. Quality… Audio